The present invention relates to marine antifouling methods, paints and compositions.
Marine fouling has plagued human beings since their first interaction with the marine environment. Marine fouling, which is the undesirable attachment of organisms to a marine surface, occurs not only on marine vessels such as ship's hulls and drive systems, but also on other structures exposed to sea water. Such structures may include: pilings, marine markers, undersea conveyances like cabling and pipes, bulkheads, cooling towers, and any device or structure that operates submerged.
Fouling is dependent upon a number of factors including light, substrate configuration and characteristics, water flow, chemical factors, biological complexity of the larva, the density and make-up of the larval community, and the presence or absence of surface films.
Surface films on marine surfaces are of great interest, because the great majority of marine larvae settle more readily on filmed surfaces. D. J. Crisp, Chemosorbtion in Marine Organisms: Factors Influencing the Settlement of Marine Invertebrate Larvae 177, 215 (1974) (ed. P. T. Grant & A. M. Mackie). Such surface films on marine structures are generated by marine microbes almost immediately upon the structure's entry into the water. D. Kirchman et al., Mar. Chem. 27:201-17 (1989).
These microbes act to stimulate further development of fouling organisms. C. E. Zobell and E. C. Allen, The Significance of Marine Bacteria in the Fouling of Submerged Surfaces, J. Bact. 29:230-51 (1935). In fact, investigators have found what appears to be a strong correlation between a primary film formation and attachment of animals to marine surfaces. R. Mitchell & L. Young, The Role of Microorganisms in Marine Fouling, Technical Report No. 3 V.S. Office of Naval Research Contract No. N00014-67-A-0298-0026 NR-306-025 (1972).
The surface films may include extracellular carbohydrates and proteins exuded by the marine microorganisms, which may be used to attach the microorganisms themselves to a marine surface. A. Danielsson et al., On Bacterial Adhesion--the effect of certain enzymes on adhered cells of a marine Pseudomonas sp., Botanica Marina 20:13-17 (1977); G. G. Geesey et al., Microscopic Examination of Natural Sessil Bacterial Populations from an Alpine Stream, Can. J. Microbio. 23:1733-36 (1977). Protein adsorption onto surfaces may have a substantial impact on microbial, chemical, and biogeochemical processes occurring at sea-water-surface interfaces. D. L. Kirchman, et al., Adsorption of Proteins to Surfaces in Seawater, Marine Chemistry 27:201-217 (1989). Such attachment provides a microorganism advantages in that it can receive a constantly renewed supply of organic nutrients within physical conditions that are conducive to growth. J. W. Costerton et al., How Bacteria Stick, Scientific American 238:86-95 (1977).
However, fouling (i.e. undesirable attachment of organisms to a marine surface) creates many problems. Fouling results in increased drag, weight and corrosion for marine structures; decreased aesthetic appearance of the marine structure; and increased maintenance costs associated with removal of the fouling and repair of the structure. Further, even a small number of barnacles or equivalent organisms attaching themselves to the propellers of a boat can significantly reduce the propellers' efficiency or create cavitation problems.
The marine industry has attempted to reduce fouling by adding various toxic materials, such as mercury, tin and copper, to the coatings of vessels and structures. However, there are significant environmental problems with the use of these additives. The coatings containing the additives are usually formulated to expose the toxic materials embedded within the coating structure to the environment. It is this exposure that allows the toxic materials to leach into the marine environment, thus reducing attachment by the crustaceans.
However, the toxic nature of the materials is a double-edged sword; these additives have a generally adverse effect upon the marine environment, beyond simply reducing attachment by the crustaceans. Because of environmental concerns associated with the use of such additives, the U.S. Environmental Protection Agency (EPA) has significantly restricted the continued use of these compounds, particularly tin and mercury. In addition, even where the use of these additives is permitted, the additives are expensive to use, requiring frequent refurbishment (in some regions as frequently as every six months). Thus, these toxic additives are costly in terms of both resources and damage to the environment. Moreover, the marine organisms that attach to the underwater surface can acquire an immunity to the toxic materials and effectively render the materials impotent.
In light of the foregoing, there is a need for marine antifouling methods and compositions that do not use toxic additives in such a way as to substantially harm the environment. After much experimentation, the inventors developed the idea of incorporating, into marine coatings, hydrolytic enzymes and/or microorganisms whose function is to limit undesirable marine fouling.
The inventors' approach offers significant advantages over previous attempts to solve marine fouling problems. For example, the inventive method relies on hydrolytic enzymes and/or living cells to prevent biofouling. Thus, the coatings of this invention can be formulated so as not to contain an appreciable amount of toxic materials (such as heavy metals), and still retain their efficacy. This avoids the environmental concerns associated with the use of heavy metal biocides.
In these embodiments of the invention, microorganisms and/or hydrolytic enzymes are embedded in marine stable coatings such as epoxy, polyurethane or other coating materials by simple mixing. The microorganisms and/or hydrolytic enzymes can be used on any surface to which the marine compositions and/or paints of the invention can bind (paddles, propellers, hulls, cooling towers, etc.). Therefore, a wide range of applications is available for the coatings and/or paints of the invention.
The use of microorganisms, in addition to use of hydrolytic enzymes, allows for further benefits. For instance, when the inventive composition and/or paint is inoculated with beneficial microorganisms, the microorganisms may excrete materials, such as additional hydrolytic enzymes, that augment the hydrolytic enzymes that may have been added to the coating and/or paint. This refurbishment may continue in a robust fashion for the life expectancy of the composition and/or paint or until the microorganism population disintegrates in the marine environment. Alternatively, the beneficial microorganisms may outcompete fouling organisms on the marine surface, thus reducing fouling.